Especially if applied in, for instance an office or a professional environment, luminaries should fulfill several requirements. Firstly, the light source should have a sufficiently long lifetime. Conventional luminaries are often based on fluorescent tubes, which have a relatively limited lifetime. In a typical office environment, the tubes themselves need to be replaced every 6000 hours. This corresponds to a replacement every 2 years, which adds to the cost of ownership.
Secondly, the light output of the luminary should be robust against dust and other dirt. A luminary that collects dust will become less efficient, since the dirt blocks light. Since cleaning the luminary is an expensive matter, the design should be robust against dust and dirt.
Thirdly, the luminary should satisfy an anti-glare requirement (i.e. the unified glare ratio should be sufficiently small). This anti-glare requirement means that the luminary should not show any bright spots. In particular, there should be no bright spots if the luminary is viewed under an oblique angle.
A luminary of the prior art is disclosed in U.S. Pat. No. 6,241,358, describing a lighting panel consisting of a set of light guide blocks in tandem arrangement, where a separate fluorescent tube provide light for each light guide block. The light from the fluorescent tubes is transmitted into the respective light guide block, is distributed therein and is transmitted through an output surface of the light guide block. However, as mentioned above, fluorescent tubes have a limited lifetime and are expensive to replace. Further, the breakdown of a single fluorescent tube in this prior art luminary has a drastic negative impact on the lighting capacity of the lighting panel and on the homogeneity of the light from the lighting panel. Thus, when one of the tubes breaks down, it will be necessary to replace this broken tube immediately.
Further, the saw tooth shaped backside of the luminary according to the '358 patent can easily trap a lot of dust and dirt, and is rather complicated to clean.
Additionally, fluorescent tubes emit a constant spectrum, which limits the color variability capacity of such a lighting panel.